Cooking utensil made from aluminum alloy strips produced by continuous thin gauge twin roll casting

ABSTRACT

The invention concerns a method for making aluminium alloy strips containing (by weight) at least 0.15 to 1.5% Fe and/or 0.35 to 1.9% Mn, with Fe+Mn&lt;2.5% and optionally Si&lt;0.8%, Mg&lt;0.2%, Cu&lt;0.2%, Cr&lt;0.2%, Zn&lt;0.2%, and other elements each &lt;0.1% and &lt;0.3 % in all, by continuous casting between two cylinders cooled and shrinked to a thickness ranging between 1 and 5 mm, the force applied to the cylinders during casting, expressed in tonnes per meter of strip width, being less than 300+2000/e, e being the cast strip thickness in mm. The invention also concerns strips in alloy of the same composition, twin-roll cast between 1 and 5 mm thick and having a product R 0.2  (MPa)×A (%) greater than 2500, and preferably than 3000.

TECHNICAL FIELD

[0001] The invention concerns a method for making aluminium alloy stripswith low magnesium and copper content, especially AlFeSi and AlMnalloys, by continuous thin gauge twin-roll casting (<5 mm). It alsorelates to strips of said alloys cast by thin gauge twin-roll casting,and optionally cold rolled, having high mechanical resistance, goodformability and good anisotropy.

STATE OF THE ART

[0002] To obtain high mechanical resistance with aluminium alloys notrequiring subsequent structural hardening, recourse is generally made tothe addition of magnesium, as for the alloys of the 5000 series as perthe Aluminium Association nomenclature. Aside from the fact that thecasting of these alloys, in particular their continuous casting, isfairly demanding, there are applications for which the presence ofmagnesium in substantial quantities is unacceptable. This is the casefor example with sheets intended for enamelled cooking utensils, inwhich magnesium has an adverse affect on the adherence of the enamellayer, or for strips intended for manufacturing heat exchanger bladesbrazed with a fluoride flux, since the magnesium diffuses on the surfaceand reacts with the flux. On this account, for these applications use ismade of the AlFeSi alloys in the 1000 series, AlMn alloys in the 3000series or AlSiFe alloys in the 4000 series whose mechanical resistanceis distinctly lower. The article by M. DELEUZE and D. MARCHIVE on thenew wrought alloys “Les nouveaux alliages de corroyage 4006 et 4007”Revue de l'Aluminium, June 1980, pp. 289-292, clearly demonstrates thedemands of the cooking utensil market placed upon aluminium alloy stripmanufacturers.

[0003] These alloy strips are usually produced by verticalsemi-continuous casting of plates, hot rolling, cold rolling and softannealing. After enamelling, involving annealing at a temperature in theregion of 550° C., or after PFTE coating submitted to polymerization ataround 450° C., the sheets of 4006 and 4007 alloys have a yield strengthR_(0.2) of between 55 and 80 MPa.

[0004] It is also possible to make strips by continuous casting, inparticular by twin-roll casting between two cooled steel cylinders.Continuous casting, inasmuch as the solidification conditions differfrom the usual process, may lead to microstructures that are also quitedifferent. U.S. Pat. No. 3,989,548 for example by Alcan, published in1976 describes (example 9) aluminium alloys containing at least one ofthe elements Fe, Mn, Ni or Si cast in strips by continuous twin-rollcasting to a thickness of 7 mm. The structure of the cast strip containsrod-like fragile intermetallic compounds with a diameter of between 0.1and 1.5 μm, which cold rolling with a reduction of at least 60% breaksdown into fine particles less than 3 μm in size. The strips obtainedoffer a good compromise between mechanical resistance and formability,but these properties only become of real interest in fairly high contentalloys for example AlFeMn alloys with Fe>1.4% and Mn>0.6%, or AlFeNialloys with Fe>1.2% and Ni>1.1%.

[0005] Patent FR 2429844 (=GB 2024870) by Norsk Hydro describes acontinuous casting method for producing alloy strips of AlMn, AlMg,AlMgSi or AlMgMn offering both good mechanical resistance and goodductility, to which less than 0.5% of anti-recrystallizing agents areadded (Zr, Nb, Ta, Hf, Ni, Cr, Ti, V or W).

[0006] U.S. Pat. No. 5,380,379 by Alcoa concerns the manufacture bycontinuous twin-roll casting of fairly high content alloy foil with 1.35to 1.6% iron, 0.3 to 0.6% manganese, 0.1 to 0.4% copper, and less than0.2% silicon. The silicon content is limited by the onset ofintermetallic phases of AlFeSi or AlMnSi type while the presence ofcopper is necessary to impart sufficient mechanical resistance to theproduct.

[0007] Conversely, patent application WO 96/27031 by Alcan concernsalloys with lower alloying content containing 0.40 to 0.70% iron, 0.10to 0.30% manganese, 0.10 to 0.25% copper and less than 0.10% silicon,obtained by continuous casting of strips having a thickness of less than25 mm, whose properties are close to those of alloy 3003. After coldrolling and annealing at between 350 and 400° C., the alloy at temper“O” (according to norm NF EN 515) shows a grain size of less than 70microns and properties very close to those of alloy 3003 produced usinga usual processing range. This kind of composition may prove to berestrictive for some applications in which lesser content alloys areused such as 1050 or copper-free alloys.

[0008] Patent EP 0039211 by Alcan describes a continuous castingmanufacturing process to a thickness of between 3 and 25 mm of AlMnalloy strips containing 1.3 to 2.3% manganese, and possibly less than0.5% iron, magnesium or copper, less than 2% zinc and less than 0.3%silicon. The processing range described is fairly complex since itcomprises homogenisation to precipitate at least one half of themanganese in intermetallic form, cold rolling with a reduction of atleast 30% and one or more intermediate annealing operations. The stripsobtained show mechanical characteristics which lead to a productA×R_(0.2), A being elongation in % and R_(0.2) being the yield strengthat 0.2% in MPa, whose value is no more than 2100.

[0009] Patent EP 0304284 by Alcan describes an alloy with high thermalstability containing from 1.5 to 2.5% manganese, 0.4 to 1.2% chromium,0.4 to 0.8% zirconium and up to 2% magnesium, and its production bycontinuous casting of strips having a thickness of less than 4 mm. Thevery unusual chromium and zirconium contents, especially when combinedwith an addition of magnesium, lead to high mechanical resistance but tothe detriment of elongation which remains less than 10%, making thesealloys unfit, even in the absence of magnesium, for the production ofcooking utensils for example.

[0010] The continuous casting of aluminium alloy strips between cooledcylinders has been known for many years. For a moderate investment costit can be used to produce a fairly wide range of alloy strips which donot require subsequent hot rolling. In recent years, considerableprogress has been made by manufacturers of casting machines to reducethe thickness of the cast strip, which can in some cases be reduced toapproximately 1 mm, thereby reducing the amount of cold rolling neededand can even do away with the latter for final gauges of >1 mm providedthat the quality of the cast strip is sufficient for intendedapplications. This progress has been the subject of several papers attechnical meetings for example

[0011] M. CORTES “Pechiney Jumbo 3 CM®. The new demands of thin stripcasting” Light Metals TMS 1995, p. 1161.

[0012] B. TARAGLIO, C. ROMANOWSKI “Thin gauge/High Speed roll castingtechnology for Foil Production” Light Metals TMS 1995, pp. 1165-1182.This article mentions a certain number of alloys which may be cast onthe described machine, for example alloys 1050, 1060, 1100, 1145, 1188,1190, 1193, 1199, 1200, 1230, 1235, 1345, 3003, 8010, 8011, 8111 and8014. The article also indicates that the force of the roll-mill usedfor continuous twin-roll casting is 3000 t, which stresses the need touse high forces for thin gauge casting.

PURPOSE OF THE INVENTION

[0013] The purpose of the invention is to obtain aluminium alloy stripswith low Mg and Cu content which, at the as-cast state or at the coldrolled state, offer mechanical resistance which is distinctly greaterthan that of similar strips having the same composition obtained byconventional casting or thick-gauge continuous casting, and which alsohave at least equivalent formability and anisotropy. A further purposeis to obtain aluminium alloy strips which recrystallize at a much highertemperature than the recrystalization temperature of the same alloysobtained by conventional casting, in particular to obtain alloys whichdo not recrystallize at the usual enamelling or PTFE polymerisationtemperature for cooking utensils.

SUBJECT OF THE INVENTION

[0014] The subject of the invention is a method for producing aluminiumalloy strips containing (by weight) at least one of elements Fe (from0.15 to 1.5%) or Mn (from 0.35 to 1.9%) with Fe+Mn<2.5%, and optionallycontaining Si (<0.8%), Mg (<0.2% preferably <0.05%), Cu (<0.2%preferably <0.1%), Cr (<0.2% preferably <0.02%) or Zn (<0.2% preferably<0.1%), the other elements being <0.1% each and 0.3% in all, bycontinuous casting between cooled shrinked cylinders, to a thickness ofbetween 1 and 5 mm, optionally followed by cold rolling, the forceapplied to the casting rolls expressed in t per metre of strip widthbeing less than 300+2000/e, e being the thickness of the strip expressedin mm. Casting is preferably made with an arc of contact of less than 60mm with slowed down heat exchange such that the temperature of thecylinder bands remains at a temperature above 80° C., preferably above130° C.

[0015] A further subject of the invention is aluminium alloy stripshaving the above composition and a gauge of between 1 and 5 mm, obtainedby continuous twin-roll casting which, at as-cast state, have a productR_(0.2)×A of >2500 (preferably >3000), R_(0.2) being the yield strengthat 0.2% of the strip expressed in MPa and A the elongation expressed as%. The strips have a yield strength R_(0.2) of more than 80 MPa, theirelongation A is greater than 20% and their earing ratio is less than 7,preferably less than 5.

[0016] Finally another subject of the invention is an AlMn alloy stripthat comes under the preceding composition (Mn>0.35%) such that the sumof the Fe+Mn contents lies between 1.4 and 2.5% (preferably between 1.5and 2%) twin-roll cast to a thickness of <5 mm and optionally coldrolled, which after enamelling or PTFE coating has a yield strengthof >80 MPa preferably >100 MPa.

DESCRIPTION OF THE INVENTION

[0017] The invention is based on the finding that a particularadjustment of the parameters for continuous thin gauge twin-roll castingcan, for alloys without heat treatment and without the addition ofmagnesium or copper, achieve a set of fully surprising mechanicalcharacteristics at the cast or cold rolled state, in particular a muchhigher yield strength than that of strips having the same compositioncast in conventional manner or by continuous thick gauge casting or bycontinuous thin gauge casting under different conditions.

[0018] The invention applies to aluminium alloys without heat treatmentand virtually free of magnesium and copper. They are mainly alloys withvery low additional element content, such as 1050 but still containingat least 0.15% iron, AlFeSi alloys possibly containing up to 1.5% ironand 0.8% silicon, such as alloys 1050, 1100, 1200, 1235, 8006 (thislatter also containing manganese), 8011 or 8079, and finally manganesealloys containing between 0.35 and 1.9% Mn, such as alloy 3003.

[0019] For alloys containing silicon, the possibility of reaching asilicon content as high as 0.8% is an advantage compared withconventional casting and enables the recycling of some alloys, such asthose used for brazed exchangers coated with an AlSi alloy. However,beyond 0.8%, the formation is observed of AlMnSI or AlFeSi primaryphases which may hinder casting, in particular due to the risk ofsolidification in the injector. There is even a risk of the onset ofprimary phases for manganese alloys when Mn exceeds 1.9% or when the sumMn+Fe exceeds 2.5%.

[0020] The strips of the invention have an original microstructure. Theaverage particle size of intermetallic iron, silicon or manganese phasesis in the region of 0.4 μm, and at least 90% of these particles are lessthan 1 μm in size. This microstructure can be seen under electronscanning microscopy on a polished metal section. To determine particlesize, digital analysis of micrographs is used to determine their surfacearea A, from which the size parameter d can be calculated using theformula d=24{square root}A/π.

[0021] The method for producing aluminium alloy strips according to theinvention will be described with reference to FIG. 1 which gives alongitudinal cross-section diagram of a continuous twin-roll castingmachine. This machine comprises a liquid metal feed (1), an injector (2)which injects the liquid metal into the space between twin cooled rolls(3 and 4). Each roll (3) and (4) comprises a cylinder body (3 a) and (4a) with a cooling water circuit leading to its surface. The cylinderbody is shrinked with a tubular shell (3 b) and (4 b) which ensuresmechanical and heat contact with the metal and may be replaced whenworn. Metal solidification is made between the rolls and a solid metalstrip (5) emerges. By arc of contact is meant the distance d separatingthe injector outlet (2) and the plane of the roll axes (3) and (4).

[0022] The alloy is cast in a strip having a thickness of between 1 and5 mm. The main condition to be heeded is to cast with relatively lowseparating force unlike the teaching of the prior art. This forceexpressed in tonnes per metre of cast strip width must remain below300+2000/e, e being the cast thickness measured in mm. Therefore for acast thickness of 2.5 mm, the force must remain lower than 1100 t permetre of width.

[0023] Other arrangements have a favourable influence on the mechanicalcharacteristics of the cast strip. For example, contrary to expectation,it is preferable that the heat exchange between the metal undergoingsolidification and the cylinder shells should not be too good. Thisleads to a high cylinder shell temperature, typically more than 80° C.,preferably more than 130° C., and can be achieved with shells in metalhaving poor thermal conductivity (for example a molybdenum steel) andrelatively thick (for example between 50 and 100 mm). Another favourablearrangement, which partly relates to the preceding arrangement, is tooperate with a rather low arc of contact, less than 60 mm, preferablyless than 56 mm. This reduces the heat exchange between the metal andthe cylinder shells and can be achieved by moving the injector close tothe rolls and/or using relatively small rolls.

[0024] These casting conditions impart upon the strip theabove-described microstructure and achieve non-recrystallization of thealloy until it reaches a temperature in the region of 380 to 400° C.,which enables high mechanical resistance for example to be maintainedafter enamelling or PTFE coating treatment for cooking Utensils producedfrom this strip.

[0025] The mechanical resistance of the alloy strips of the invention,at the as-cast state, is distinctly greater than that of strips in thesame alloy and of the same thickness obtained by conventional platecasting with hot and cold rolling, and even of strips made by continuouscasting under different casting conditions. The yield strength, for allthe alloys of the invention, is always higher than 80 MPa and most oftenmore than 100 MPa, in particular for the manganese alloys. Goodformability is also achieved with elongation that is always greater than20% (and 30% for Mn-free alloys such as 1050 or 1200) and above allthere is particularly favourable compromise between yield strength andelongation measured by the product R_(0.2)×A (R_(0.2) expressed in MPaand A in %), this product being at all times more than 2500, and mostfrequently more than 3000. Good anisotropic properties are also obtainedwith an earing ratio that is always less than 7, and most often lessthan 5.

[0026] The mechanical characteristics are measured in the lengthdirection in accordance with standard EN 10002. The earing ratio ismeasured in accordance with standard NF-EN 1669 with a stamping ratio ofbetween 1.8 and 1.95, preferably 1.92, and is expressed (as %) by theratio 2×(mean height of 4 ears−mean height of 4 troughs)/(mean height of4 ears+mean height of 4 troughs), the anisotropy of the this type ofalloy generally being of 4 ear type at 45°.

[0027] For manganese alloys with Mn+Fe>1.4%, after annealing up to 550°C. (for example enamelling and PTFE annealing) a yield strength of >80MPA is obtained most often >100 MPa.

[0028] After one or more cold rolling passes, the strips of theinvention have a yield strength R_(0.2) that is significantly muchhigher than that of strips produced by conventional casting andsubjected to the same work hardening. The yield strength after workhardening is usually expressed by a work hardening law according to theformula

R _(0.2) =kε ^(n) where ε=(2/{square root}3)ln (initial thickness/finalthickness)

[0029] the initial thickness being the as-cast thickness for continuousstrip casting, and the strip thickness at the last recrystallizationannealing for strips produced by conventional casting from plates andhot rolled. For cold rolled strips of the invention with a reductioncoefficient of no more than 60%, that is to say for ε values lyingbetween 0 and 1, the k coefficient is always greater than 150, whereasit is less for strips produced by conventional casting, and n is lowerthan 0.20 (and most often than 0.15) whereas it is greater than 0.20 forstrips produced by conventional casting.

[0030] This set of properties is particularly advantageous for theproduction of drawn cooking utensils for which it is necessary to usemagnesium-free alloys. With this thin-gauge casting it is possible touse as-cast strips, which offer an advantageous cost price, and the heattreatments involved for enamelling and coating with anti-adhesiveproducts such as polytetrafluorethylene (PTFE) do not lead to a loss inmechanical characteristics. These properties are also of interest forthe production of fins for heat exchangers, in particular for radiatorsor motor vehicle air conditioning systems intended to be assembled withtubing by brazing with a non-corrosive flux. Here again the presence ofmagnesium is unacceptable and furnace brazing does not lead to anyreduction in mechanical characteristics. Finally, they are also ofinterest for the production of varnished or lacquered products whichneed to undergo heat treatment for the coating.

EXAMPLES Example 1 Influence of the Separating Force

[0031] On a continuous twin-roll 3CM casting machine made by PechineyAluminium Engineering, 5 alloys were cast whose chemical composition (byweight %) is given in table I: TABLE I Alloy Mn Fe Si Mg 8006 0.44 1.290.15 0.028 3003 1.1  0.40 0.10 — 1050 — 0.20 0.14 0.002 8011 — 0.75 0.70— 1200 — 0.55 0.20 —

[0032] In each case, measurements were taken of cast thickness,separating force per metre of strip width, compared with the limit valueof 300-2000/e, and the mechanical characteristics of the as-cast striptensile strength R_(m) (in MPa), yield strength at 0.2% R_(0.2) (inMPa), elongation A (%) and earing ration (%) according to standard NF-EN1669 with a drawing ratio of 1.92. The results are grouped together intable II: TABLE II e Force 300 + R_(m) R_(0.2) A R_(0.2) × Earing Alloymm t/m 2000/e MPa MPa % A ratio 8006 3.1  867 945 166 118 25 2950 2.83003 3.0  900 967 158 114 23 2622 4.4 1050 3.5  720 871 106  81 39 31594.0 8011 3.9 1018 813 156 112 23 2576 9.0 1200 3.0 1100 967 121  93 322976 8.9 3003 3.5 1400 871 181 141 17 2297 8.0

[0033] It is found that, in the first 3 cases, both an elongation ofmore than 20% and a product R_(0.2)×A of more than 2500 is obtained,together with an earing ratio of less than 7. On the other hand, for the3 last cases in which the force is too high, the earing ratio is quitesubstantial which renders the strip unfit for stamping.

Example 2 Influence of Cylinder Band Temperature

[0034] For alloys 1050 and 3003 a comparison was made of the mechanicalcharacteristics of the cast strips at respective cylinder shelltemperatures of 130° according to the invention) and 700 (outside theinvention). The results are given in table 3: TABLE III e R_(m) R_(0.2)A R_(0.2) × Alloy (mm) temp (°) (MPa) (MPa) (%) A 1050 3 130 106  81 393159 1050 3  70 105  80 29 2320 3003 3.5 130 158 114 23 2622 3003 3  70149 114 18 2052

[0035] It is found that a high cylinder shell temperature contributes toincreasing elongation without detriment to mechanical resistance.

Example 3 Influence the Arc of Contact and Separating on Earing Ratio

[0036] The earing ratio was measured on strips cast to differentthicknesses with different separating forces and arcs of contact ofdifferent lengths. The results are grouped together in table IV. TABLEIV e Force 300 + 2000/e Arc of Earing Alloy mm t/m t/m contact mm ratio8006 3.1 867 943 45 2.8 3003 3.0 937 967 45 3.2 8006 3.2 867 925 45 3.28006 3.1 833 945 45 2.4 3005 3.0 567 967 45 1.5 3005 2.35 833 1151 451.7 1050 1.95 727 1326 45.5 6.3 1050 1.7 767 1476 45.5 6.7 1050 4.0 930800 52 4.7 1050 3.0 920 967 52 6.0 1050 3.1 1253 945 70 8.5 1050 3.5 720871 53 4 8011 3.9 1019 813 57 9.0 1200 4.15 780 782 58 6.5 1200 4.15 769782 58 5.4 1200 3.6 1055 856 62 8.8 8011 3.8 1440 826 55 7.5 8011 3.71440 841 56 8.2 1200 3.0 1230 967 55 12 8011 3.8 1104 826 57 7.6 80113.35 850 901 56 5.2 8011 3.55 979 862 56 9.5 8011 3.65 925 849 57 9.6

[0037] It is found that there is no correlation between the castthickness and the earing ratio, but that high earing ratios (>7)correspond to high forces (>300+2000/e) and/or high arcs of contact (>56mm).

Example 4 Mechanical Characteristics after Enamelling and PTFE Coating

[0038] For the different alloys of the invention measurements were madeof the mechanical characteristics at as-cast state, after anti-adhesivePTFE coating comprising resin polymerisation annealing at 420° C. andafter enamelling comprising an enamelling annealing at 560° C. Theresults after heat treatment were compared with those obtained withalloys 4006 and 4007 which underwent conventional processing, and whichare the alloys with the highest performance used for the production ofenamelled or PTFE coated cooking utensils. The results are given intable V: TABLE V After PTFE After Crude cast coating enamelling e R_(m)R_(0.2) A R_(m) R_(0.2) A R_(m) R_(0.2) A All mm MPa MPa % MPa MPa % MPaMPa % 3003 3.0 158 114 22 154 110 23 148 105 26 3003 3.5 181 141 17 173136 20 156 111 25 8006 3.1 166 118 25 151 108 27 132  85 32 8011 3.9 156112 23 139  75 28 125  36 36 1200 3.0 121  93 32 100  64 34  80  20 504006 120  55 48 142  59 42 4007 161  68 30 173  76 26

[0039] It is found that after PTFE coating, the alloys with lesseralloying content 1200, 8006 and 8011 made with continuous castingaccording to the invention still show a yield strength that iscomparable with that of alloys 4006 and 4007 specially designed fortheir resistance to high temperatures. After enamelling, alloy 3003according to the invention shows a much higher yield strength than thatof alloys 4006 and 4007 made by conventional casting whereas thesealloys are specially designed for enamelling.

Example 5 Work Hardening Laws

[0040] The work hardening curves were compared of alloys 1200 and 3003produced by conventional casting and by continuous casting according tothe invention, from an initial thickness of 3 mm up to final thicknessesreaching 1.25 mm, that is to say for values e lying between 0 and 1. Therespective values of the k and n coefficients for the curveR_(0.2)=kε^(n) are given in table VI: TABLE VI Alloy cast k n 1200invention 169 0.13 1200 conventional 105 0.21 3003 invention 229 0.123003 conventional 150 0.22

[0041] It is found that for the strips of the invention in the domainunder consideration, k is higher and n is lower, which leads to greaterwork hardening since ε<1 and n<1.

1. Method for producing aluminium alloy strips containing(by weight) at least one of elements Fe (from 0.15 to 1.5%) or Mn (from 0.35 to 1.9%) with: Fe+Mn<2.5%, and optionally containing Si (<0.8%), Mg (<0.2%), Cu (<0.2%), Cr (<0.2%), Zn (<0.2%), other elements <0.1% each and 0.3% in all, by continuous twin-roll casting between cooled shrinked cylinders to a thickness of between 1 and 5 mm, optionally followed by cold rolling, the force applied to the rolls during casting, expressed in t per metre of strip width, being less than 300+2000/e, e being the thickness of the cast strip expressed in mm.
 2. Method for producing aluminium alloy strips containing (by weight) at least one of elements Fe (from 0.15 to 1.5%) or Mn (from 0.35 to 1.9%) with Fe+Mn<2.5%, and optionally Si<0.8%, Mg <0.2%, Cu <0.2%, Cr<0.2%, Zn<0.2%, other elements <0.1% each and 0.3% in all, by continuous twin-roll casting between cooled shrinked cylinders, characterised in that the heat exchange between the metal and the cylinder shells during casting is slowed down such that the temperature of the cylinder shells is higher than 80° C., preferably than 130° C.
 3. Method in accordance with claim 2, characterised in that the cylinder shell material has poor thermal conductivity.
 4. Method according to any of claims 1 to 3, characterised in that the arc of contact between the metal and the casting rolls is less than 60 mm, preferably less than 56 mm.
 5. Aluminium alloy strip containing (by weight) at least one of elements Fe (from 0.15 to 1.5%) or Mn (from 0.35 to 1.9%) with Fe+Mn<2.5% and optionally containing Si (<0.8%), Mg (<0.2%), Cu (<0.2%) or Zn (<0.2%), other elements <0.1% each and 0.3% in all, continuous cast to a thickness of between 1 and 5 mm, having at the as-cast state a product R_(0.2) (in MPa)×A (%) greater than
 2500. 6. Strip according to claim 5 having a product R_(0.2)×A greater than
 3000. 7. Strip according to either of claims 5 or 6 having a yield strength R_(0.2) greater than 80 MPa.
 8. Strip according to claim 7 having a yield strength R_(0.2)>100 MPa.
 9. Strip according to any of claims 5 to 8, having an elongation A>20%.
 10. Strip in Mn-free alloy according to claim 9 having an elongation A>30%.
 11. Strip according to any of claims 5 to 10, having an earing ratio of less than
 7. 12. Strip according to claim 11, having an earing ratio of less than
 5. 13. Strip according to any of claims 5 to 12, characterized in that the average size of the intermetallic particles containing Fe, Mn and/or Si is no more than 0.4 μm.
 14. Strip according to any of claims 5 to 13, characterized in that the size of at least 90% of the intermetallic particles containing Fe, Mn and/or Si is less than 1 μm. 15 Strip in Al-Mn alloy according to any of claims 5 to 14 with Fe+Mn>1.4% having, after enamelling and/or PTFE anti-adhesive coating treatment, a yield strength of more than 80 MPa, preferably more than 100 MPa.
 16. Strip cold rolled from a strip according to any of claims 5 to 15, characterized in that the k and n coefficients of the work hardening curve R_(0.2)=kε^(n), in which ε=(2/{square root}3)l_(e) (initial thickness/final thickness) are such that k>150 and n<0.20.
 17. Strip according to claim 16, characterized in that n<0.15.
 18. Enamelled and/or PTFE anti-adhesive coated cooking utensil produced from strips according to any of claims 5 to
 17. 19. Lacquered or varnished strip according to any of claims 5 to
 17. 